Catheters find their use in many different medical applications, such as urinary catheters for bladder drainage. Each catheter is normally pre-packed in a receptacle by the manufacturer, in order to maintain the catheter in a clean and preferably sterile condition.
A urinary catheter in general need to have a lubricant applied to the outer surface thereof to facilitate insertion into the urethra. Especially, for lubrication purposes, a hydrophilic urinary catheter may have a hydrophilic outer surface coating or layer which should be wetted by a fluid such as water for a certain time period prior to insertion of the catheter into the urethra of a patient. In order to facilitate the use and to improve cleanliness of the catheter, the assemblies have in recent years developed to comprise a rupturable wetting fluid pouch or container as well. Such assemblies are disclosed in e.g. WO 97/26937, WO 01/43807 and WO 98/11932.
Further, there has been a trend towards so-called “ready-to-use” catheters, where the catheter is arranged in the receptacle together with a wetting fluid in such a way that the catheter is maintained in a wetted, activated condition by said fluid. Such ready-to-use catheter assemblies are disclosed in e.g. WO 00/47494 and WO 98/19729.
A well-recognized problem with hydrophilic coatings or layers has been that the hydrophilic polymer surface may lose water and dry out when it comes in contact with e.g. a mucous membrane, such as when the catheter is inserted into the urethra. This occurs because of a difference between the osmotic potential of the hydrophilic surface and the osmotic potential of the mucous membrane. The mucous membrane has a higher osmotic potential, i.e. a higher salt concentration, than the hydrophilic surface. This difference in osmotic potential causes the water to go from the hydrophilic surface layer to the mucous membrane so that the difference in the salt concentration will be counter-balanced. Naturally, this affects the low-friction properties of the hydrophilic outer surface coating, and may lead to pain and injuries of the patient.
For this reason, the present applicant has previously developed an improved hydrophilic coating, in which an osmolality-increasing compound was applied to a non-reactive hydrophilic polymer surface, thereby producing a more stable hydrophilic surface, as is disclosed in EP 217 771. Hereby, the theretofore prevailing problem of the hydrophilic coating drying out when inserted into the urethra, thus rendering the article insufficiently hydrophilic, was alleviated.
Similar hydrophilic coatings incorporating an osmolality-increasing compound are discussed in WO 94/16747 disclosing a process in which the osmolality-increasing compound is added during the process of applying the hydrophilic coating to the base material, EP 586 324 and EP 591 091 disclosing a hydrophilic coating comprising a non-dissolved, solid osmolality-increasing compound e.g. in the form of a powder or grain, and EP 991 702 disclosing a cross-linked hydrophilic coating comprising a water soluble osmolality-increasing compound.
However, these known methods and coatings are affected by some problems. For example, the production processes, involving different manners of incorporating the osmolality-increasing compounds in the coatings, are rather tedious cumbersome and costly. Further, the properties of the resulting, wetted hydrophilic surface coating to be inserted into the patient are, at least to a certain extent, affected by parameters of the wetting process, such as the quantity of wetting fluid used for the wetting, the constituents of the chosen wetting fluid, and the time period during which the wetting is carried through. Since several such parameters may be unknown beforehand, and may vary to a significant degree, the properties of the resulting, activated coating become unpredictable as well.
WO 00/47494 discloses a ready-to-use catheter product in which a wetting fluid is arranged in a receptacle in direct contact with a hydrophilic surface of a catheter, thereby continuously maintaining the hydrophilic surface in an activated state. This document discloses the use a saline solution as the wetting fluid. However, no information is given about any specific concentration of salt in the wetting fluid.